JPH0542287B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for separating two or more volatile components in a liquid in a gas phase using a permselective membrane. Concerning energy saving methods.

[Conventional technology]

Methods for separating components in a liquid containing two or more volatile components based on their volatility differences have long been known as distillation methods, rectification methods, etc., and are widely used industrially. Are known.

A method of separating a plurality of components in a liquid from each other using a permselective membrane is also well known and has already been put into practical use. Recently, a method has also been reported in which gas components consisting of a plurality of components are separated from each other using a membrane having selective permselectivity. However, this latter method has not yet been put into practical use on an industrial scale.

Methods of distilling or evaporating a liquid by heating it with a heat exchanger have been known for a long time and are widely practiced.

The thermodynamic phenomenon that pressure and temperature increase when a gas is compressed adiabatically has been known for a long time.

However, vaporization of liquid by heat exchange heating,
By cleverly combining the increase in pressure and temperature through adiabatic compression of the gas and the mutual separation of multiple gas components through selective permeation film formation, heat is efficiently recovered and recycled for use, which reduces the amount of heat used. No improved separation systems are known.

[Problem that the invention seeks to solve]

Therefore, the present invention efficiently circulates and uses heat by skillfully combining liquid evaporation through heat exchange heating, pressure and temperature increase through vapor compression, and mutual separation of multiple gas components through a selectively permeable membrane. The present invention aims to provide an energy-saving volatile component separation system, ie, a separation method, and a separation device that enable the separation of volatile components.

[Means for solving problems]

The above purpose is to (1) heat and evaporate a raw material liquid containing two or more types of volatile components in a method for mutually separating volatile components in a liquid containing two or more types of volatile components; (2) compressing the vapor mixture to increase its temperature and pressure; and (3) compressing the compressed vapor mixture into the mixture. (4) A partition wall capable of heat exchange with at least one of the fractions, which is separated into a membrane-permeable fraction and a non-membrane-permeable fraction by being applied to a membrane having selective permselectivity for the constituent components of the vapor. (5) use the heat possessed by the fraction as a heat source for evaporation of the liquid component by bringing the fraction into contact with the raw material liquid of step (1); A method comprising the step of recovering one or both of the fractions;
and an apparatus for mutually separating volatile components in a liquid containing two or more types of volatile components,
(1) One or more heat exchangers into which the fraction separated by the membrane separator described in (3) below is introduced, a raw material liquid supply section, an evaporation residual liquid discharge section, and in some cases auxiliary heating (2) a compressor for compressing the mixed vapor generated from the evaporator; and (3) a component of the mixed vapor to which the mixed vapor compressed by the compressor is applied. This is achieved by a device having a membrane separator with a membrane that is permselectively permeable.

[Action and effect]

According to the present invention, a raw material liquid is evaporated by heating with a heat exchanger, this vapor is compressed to increase its pressure and temperature, and this increased pressure is used as a driving force for membrane separation. ), and on the other hand, the increased temperature, i.e. the temperature difference between the temperature of the compressed vapor (membrane-permeable fraction and/or non-membrane-permeable fraction) and the evaporation temperature of the raw liquid. The amount of heat contained in the steam can be efficiently recovered via a heat exchanger and used as part of the heat of evaporation for evaporating the raw material liquid.
Therefore, a large portion of the heat required to vaporize the feedstock liquid can be recycled and used to provide the energy (usually electricity) for operating the compressor to compress the vapor to bring the feedstock liquid above its evaporation temperature. The separation system of the present invention is extremely advantageous from an energy economic point of view because a relatively small amount of energy, such as heat to raise the temperature to the desired temperature and heat for auxiliary heating of the evaporator, needs to be supplied from the outside. It is.

[Specific explanation]

In the method of the present invention, since a mixture of volatile components is separated from each other in the gas phase by a permselective membrane, it is not necessary that the components to be separated have different volatilities; Mixtures of various components can be separated. As a mixture system that can be separated by the method of this invention, for example, a mixture system of water and organic matter is water/
Methanol, water/ethanol, water/propanol, water/butanol, water/acetone, water/acetic acid,
water/acetonitrile, water/acrylonitrile,
Examples include water/benzene, water/ethyl acetate, water/carbolic acid, and the like. Furthermore, the method of the present invention can also be used to separate organic mixtures, and in this case, the mixture system to be separated is, for example, acetate/
Various systems such as n-hexane, ethanol/acetone, styrene/ethylbenzene, benzene/aniline, etc. can be mentioned.

The evaporator used in the present invention has one or more internal heat exchangers, a liquid raw material supply section, an evaporation residue discharge section, and optionally an auxiliary heater. In the method of the present invention, since the components are not separated from each other using differences in volatility, it is not necessarily necessary for the evaporator to have a distillation separation function, and therefore a conventional evaporator is used. be able to.

In the method of the present invention, the pressure and temperature of the vapor generated in the evaporator are increased by pressurizing the vapor. The vapor compressor used for this purpose may be arbitrarily selected from compressors commonly used for compressing high-temperature vapor. Examples of such a compressor include a Roots blower compressor, an axial blower compressor, and the like.

Next, the mixed vapor compressed as described above is fractionated into a membrane permeable fraction and a membrane non-permeable fraction using a selectively permeable membrane using the increased pressure as a driving force. do. The type of permeable membrane for this purpose must be selected depending on the type, concentration, etc. of the components to be separated. For example, when separating a mixture of water and ethanol, it is advantageous to use a membrane that preferentially allows ethanol to pass through, such as silicone rubber, if the ethanol content is low; If the amount is small, it is advantageous to use a membrane that allows water to permeate preferentially, such as a cellulose acetate membrane, a polyphenylene oxide membrane, a polyimide membrane, or a silica-alumina microporous membrane.

In general, except for special membranes such as silicon membranes, the permeation rate of water is much faster than that of organic substances, and water is concentrated on the permeate side and the ethanol concentration on the non-permeate side becomes high. In particular, polyimide membranes have a high water permeation rate and a high degree of separation between water and organic vapor, and can be suitably used in the process of the present invention. At this time, the higher the pressure on the high pressure side and the lower the pressure on the low pressure side, the faster the water permeation rate becomes.

In addition, the higher the concentration of water in the feed liquid, the faster the permeation rate.To prevent condensation of concentrated water on the low pressure side,
Purging the low pressure side with an inert gas (N ₂ , air, etc.) is a common practice.

The separation membrane of the present invention is preferably a membrane that can be used at temperatures of 80°C or higher, but polyimide membranes with temperatures of 100°C or higher are preferable.
It is suitable for use at temperatures above .degree. Particularly preferred is an aromatic polyimide film comprising an aromatic tetracarboxylic acid or its dianhydride and an aromatic diamine. Polyimide membranes also have excellent membrane performance, with a water permeation rate P′ _H2O of 0.5 to 5, depending on operating conditions.
×10 ^-5 cc/cm ² ． sec.cmHg, preferably 0.1-5×
10 ^-3 cc/cm ² . sec.cmHg, and the separation performance is P′ _H2O /
P′ _EtOH is as high as 50-400, preferably 100-300.

As for the shape of the membrane, flat membranes, hollow membranes, tupular membranes, etc. can be used, and hollow membranes are particularly effective.

Next, of the vapor fractions fractionated in this way, the non-permeated fraction (sometimes referred to as the high-pressure fraction, high-pressure side, etc.) is still at high temperature and high pressure, while the permeated fraction has a low pressure. Although the temperature has decreased, the temperature is still high. Therefore, separately,
Alternatively, only one of them is introduced into the heat exchanger in the evaporator, and the heat contained therein is recovered and reused as heat for evaporating the raw material liquid.

Next, embodiments and operating principles of the method of the present invention will be explained in more detail with reference to the drawings. A raw material liquid containing at least two types of volatile components is introduced into the evaporator 1 from a raw material supply section 11 in FIG. Next, the raw material liquid is heated and evaporated by passing a heat source such as steam through the preheater 9. While the steam generated from the evaporator 1 passes through a steam conduit and a droplet separator 2, droplets accompanying the steam are separated. This vapor is compressed by a vapor compressor 14 driven by a motor 15 and supplied to the membrane separator 3. The membrane separator 3 has a high pressure section 5,
and a low pressure section 6, and a permselective membrane 4 separating the two, the high pressure section 5 being maintained at a desired high pressure by adjusting the valve 18, while the low pressure section 6 is maintained at a desired high pressure by adjusting the valve 13.
By opening, for example, the pressure is brought to atmospheric pressure, or the required degree of vacuum is maintained. This pressure difference separates the components in the vapor into a permeated fraction and a non-permeated fraction. The apparatus of the present invention is preferably entirely insulated by heat insulating material, and the vapor is nearly adiabaticly compressed by the compressor 14, so that the temperature of the vapor is lower than the evaporation temperature in the evaporator 1. will also rise considerably. This temperature is substantially maintained in the non-permeated fraction vapor and the permeated fraction vapor after passing through the membrane separator 6. These fractions can therefore be fed to the heat exchangers 7 and/or 8 in the evaporator 1 and their heat of condensation can be used as part of the heat of vaporization of the raw liquid in the evaporator 1. Therefore, when starting up, it is necessary to supply heat from the auxiliary heater 9, but once started, there is no need to supply heat from the auxiliary heater in addition to the energy added to the system by the compressor 14. Or, if necessary, the amount may be extremely small.

Evaporation in the evaporator 1 can be performed batchwise or continuously. When performing the batch process, the liquid raw material is introduced into the evaporator 1 via the raw material supply section 11 and the raw material supply valve 16, and the evaporation is performed by closing both the valve 16 and the evaporation residual liquid discharge valve 17.
After the desired volatile components have been evaporated, both valves 16 and 17 are opened to discharge the evaporation residual liquid. If the feed liquid consists essentially only of volatile substances and all of these are evaporated, it is not necessary to drain the residual liquid every minute. When evaporation is performed continuously, the raw material liquid is supplied from the evaporator 1 to the valve 16 and the raw material liquid supply section 11 at a constant flow rate suitable for supplementing the evaporated components.
The evaporator 1 is continuously supplied to the evaporator 1 via the evaporator 1, and the evaporation residue is continuously discharged to the evaporation residue discharge part and via the valve 17. If the raw material liquid consists essentially only of volatile components and all of them are evaporated, it is not necessary to continuously discharge the evaporation residual liquid. Semi-continuous operation can also be performed by intermittently supplying the raw material liquid and/or discharging the evaporation residual liquid.

Next, the heat balance in a steady state when the method of the present invention is carried out continuously will be explained in more detail. The heat introduced into the system of the present invention consists of the heat introduced by the feed liquid, the heat introduced by the compressor 14, and the heat introduced by the auxiliary heater 9, while the heat exhausted from the system consists of the heat introduced by the feed liquid, the heat introduced by the compressor 14, and the heat introduced by the auxiliary heater 9. It consists of heat carried out by the condensed separated liquid (product) discharged from the heat exchanger in the heat exchanger, heat carried out by the evaporation residual liquid, and heat loss released from the surface of the apparatus to the outside of the system. Now, the heat given to the raw material liquid by the heat exchanger 7 and/or 8 in the evaporator 1 (i.e., the heat of condensation of the separated fraction vapor) is the heat necessary to evaporate the raw material liquid in the evaporator 1. If the amount of heat is less than , it is necessary to compensate for the lack of heat with the auxiliary heater 9. In such a case, the temperature of the raw material liquid supplied to the evaporator 1 may be considerably low. Note that the auxiliary heating device 9 does not necessarily need to be provided in the evaporator 1, and may be provided as an external heater for heating the raw material liquid supplied into the system. This means that a steady state can be maintained by appropriately adjusting the temperature of the supplied raw material liquid.

Next, from the membrane separator 3 to the heat exchanger 7 in the evaporator 1
and/or the heat of condensation of the steam supplied to the evaporator 8 may be greater than the heat required to evaporate the raw material liquid in the evaporator 1. This occurs when there is a lot of heat brought in by the raw liquid, i.e. when the temperature of the supplied raw liquid is high, and when the vapor compressor 14
This can occur when a large amount of heat is introduced into the system. In this case, the steady state is restored by lowering the temperature of the supplied raw material liquid.
Alternatively, the heat exchanger 7 in the evaporator 1 and/or
Alternatively, the fraction (product) discharged from 8 can be taken out without being completely condensed and this product can be cooled by an external cooler (not shown).

Note that the temperature of the discharged product and evaporation residual liquid is quite high, so these should be supplied to another heat exchanger (not shown in the diagram) to heat the supplied raw material liquid outside the system. You can also do it.

Example 1 Ethanol Condensation Ethanol water at a concentration of approximately 80% is used to purify a water-containing organic solid such as brown sugar (cane sugar).
Ethanol water with a concentration of approximately 60% is recovered. This recovered ethanol water contains water, sugar, ash, pigment, and other impurities contained in the raw sugar. Therefore, in order to use the recovered ethanol water again, these impurities must be removed and the water must be concentrated to an ethanol concentration of 80% or more. For this reason, ethanol was concentrated using the method of the present invention.

100 raw materials ethanol water (ethanol 60,
Water 40) was prepared using the equipment schematically shown in Figure 1.
Steam is passed through the auxiliary heater 9 until the temperature of the raw material liquid reaches approximately 86°C.
When heated to ℃, evaporation began. After that, add raw ethanol water at 20/hour (ethanol 12/hour).
The evaporation residue was supplied at a constant rate of 3/hour (ethanol 0.07/hour), water 8/hour), and ethanol 0.07/hour.
water, sugar, ash, etc.).
Approximately 100 Kcal/hour of heat was supplemented by steam from the auxiliary heater 9.

17/hour raw material liquid (ethanol) at 1 atm
11.93/hour, equivalent to 5.07/hour of water) was evaporated.
In this case, the heat required for evaporation is approximately 5610 Kcal/hour. When this steam was compressed to 1.5 atmospheres using a vapor compressor equipped with a 1.1KW shaft horsepower motor, the temperature rose to 119℃. The energy introduced by this compressor is approximately 950 Kcal/hour. This compressed vapor is transferred to a silica film with a membrane area of approximately 1 ^m2 .
It was flowed along the surface of the alumina-based microporous membrane at a flow rate of 1.5 m/sec. This separates the membrane non-permeable fraction vapor and the membrane permeable fraction vapor, which are introduced into a heat exchanger in a separate evaporator, and from the outlet of the heat exchanger, the condensate from the membrane non-permeable fraction is 13/hour (ethanol 11.91/hour, water 1.09/hour, ethanol concentration approximately 84%), and condensate from the membrane permeation fraction 4/hour.
hours (ethanol 0.02/hour, water 3.98/hour, ethanol concentration 0.5%) were obtained.

In the above heat exchange, approximately
3050Kcal/hour of heat was recovered, and approximately 2440Kcal/hour of heat was recovered from the membrane permeation fraction (total approx.
5490Kcal/hour). Therefore, approximately 90% of the heat required to evaporate the raw material ethanol aqueous solution can be covered by the recovered heat, resulting in approximately
1050Kcal/hour heat (approximate heat from auxiliary heater)
100Kcal/hour and heat (power) from vapor compressor
By consuming approximately 950 Kcal/hour], it was possible to process 20/hour of raw materials.

Example 2 Concentration of ethanol When attempting to produce ethanol by fermentation, a fermented liquor with an alcohol concentration of around 10% is obtained. Therefore, ethanol was concentrated using the method of the present invention using a 10% aqueous ethanol solution as a model liquid.

The same operation as in Example 1 was performed. however,
The evaporation temperature of the raw material liquid was close to 100°C, and the entire amount of the feedstock was evaporated without discharging the evaporation residue. In this case, the heat required for evaporation is approximately
It is 11556Kcal/hour. Heating with an auxiliary heater was not performed. In addition, the steam is compressed using a compression pump with a 4.5KW shaft horsepower motor.
The pressure was set to 1.5 atm. In this case, the energy introduced into the system by the vapor compressor is approximately 3900 Kcal/hour. This increased the temperature of the steam to approximately 139°C.
A condensate of 13/hour (ethanol concentration of 0.1% or less) was obtained from the membrane-permeable fraction, and a condensate of 7/hour (ethanol concentration of 30% or more) was obtained from the membrane-unpermeable fraction. The heat recovered by the heat exchanger in the evaporator from the fraction from the membrane separator is recovered from the non-membrane fraction.
378Kcal/hour, from the membrane permeation fraction
It was 10,500Kcal/hour (total 10,898Kcal/hour).
Therefore, approximately 94% of the heat required for the evaporation of the raw material liquid
% could be covered by the recovered heat, and as a result, it was possible to process 20 Kcal/hour of raw material liquid with approximately 3900 Kcal/hour of heat supplied by the vapor compressor.

Example 3 Dehydration of Acrylonitrile Although approximately 3% water is soluble in acrylonitrile, acrylonitrile used as a raw material for synthetic fibers must be substantially anhydrous. Therefore,
The dehydration of acrylonitrile containing saturated water (approximately 3%) was carried out by the method of the invention.

The same operation as in Example 1 was performed. However, the raw material liquid was supplied at a rate of 40/hour and was completely evaporated. The evaporation temperature in this case was 24°C, and the heat of evaporation was 23,400 Kcal/hour. The steam was compressed to atmospheric pressure by a vapor compressor with a 2.5KW shaft horsepower motor. In this case, the heat introduced into the system by the compressor is 2150 Kcal/hour, and the temperature of the steam is
The temperature rose to 100℃. This compressed vapor was fractionated using a silica-alumina microporous membrane. Water was obtained at 1.2/h from the membrane permeation fraction, which did not contain detectable amounts of acrylonitrile. On the other hand, the non-permeable fraction yielded 38.8 acrylonitrile/hour, which did not contain detectable amounts of water. The heat recovered by the heat exchanger in the evaporator is approximately
720Kcal/hour, approximately 7436Kcal/hour from membrane non-permeable fraction
hours (total 8156 Kcal/hour). Therefore, approximately 35% of the heat required to evaporate the raw material liquid is covered by recovered heat, which is then introduced by the vapor compressor.
With heat of 2150Kcal/hour, 40/hour of raw material liquid could be processed.

Example 4 Concentration of ethanol 400 ethanol aqueous solution (ethanol 40+
Fill the device with water (360% water, 10% ethanol concentration),
When steam was passed through an auxiliary heater to heat the raw material until it reached 99°C, evaporation began.

Thereafter, the raw material ethanol water was constantly and continuously supplied at a rate of 200/hour (ethanol 20/hour + water 180/hour), and the entire amount was evaporated. In this case, the amount of heat required for evaporation is approximately 113,000 Kcal/hour. When this steam was compressed to 1.7 atmospheres using a vapor compressor equipped with a 22KW shaft horsepower motor, the temperature rose to 146℃. The energy introduced by this compressor is approximately 19000 Kcal/hour. This compressed vapor was passed through a separation membrane module equipped with a hollow polyimide membrane having a membrane area of about 50 m ² at a flow rate of about 1.0 m/sec. This separates the membrane non-permeable fraction vapor and the membrane permeable fraction vapor, which are each separately introduced into a heat exchanger in the evaporator, and from the outlet of the heat exchanger,
Condensate from the non-membrane fraction 35/h (ethanol
21/hour + water 14/hour, ethanol concentration approximately 60%),
And 165/hour of condensate from the membrane permeation fraction (ethanol, Negurijiguru, water 165/hour, ethanol concentration 0.1% or less) was obtained.

In the above heat exchange, approximately
Approximately 12,000 Kcal/hour of heat is recovered from the membrane permeation fraction.
94000Kcal/hour of heat was recovered (total approx.
106000Kcal/hour). Therefore, approximately 94% of the heat required to evaporate the raw material ethanol aqueous solution can be covered by the recovered heat, resulting in approximately
By consuming 18900 Kcal/hr of heat (all from the vapor compressor) it was possible to process 20/hr of feedstock.

The above separation membrane is a membrane of aromatic polyimide made from aromatic tetracarboxylic acid and aromatic diamint, and its water permeation rate P' _H2O is 3×10 ^-3 cc/cm ² . sec.
cmHg or higher, and the separation performance P′ _H2O /P′ _EtOH was 200 or higher.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the principle of the method of the present invention. In the figure, 1 is an evaporator, 3 is a membrane separator, 4 is a permselective membrane, 5 is a high pressure section, 6 is a low pressure section, 7 and 8 are heat exchangers, 9 is an auxiliary heater, and 14 is a vapor compressor. It is.

Claims (1)

[Claims] 1. A method for separating volatile components from each other in a liquid containing two or more volatile components, including: (1) a raw material liquid containing two or more volatile components; (2) compressing the vapor mixture to increase its temperature and pressure; (3) converting the compressed vapor mixture into the vapor mixture; (4) separating the membrane-permeable fraction and the non-membrane-permeable fraction by applying the membrane to a membrane having selective permeability to the constituent components of the mixed vapor; (5) using the heat possessed by the fraction as a heat source for evaporation of the liquid component by bringing it into contact with the raw material liquid of step (1) through the membrane-permeating fraction and the membrane-non-permeating fraction; A method comprising the steps of recovering one or both of the components. 2. The method according to claim 1, wherein the membrane is a polyimide membrane. 3. An apparatus for mutually separating volatile components in a liquid containing two or more types of volatile components, wherein (1) the fraction separated by the membrane separator described in (3) below is introduced. an evaporator with one or more heat exchangers, a feed liquid supply, an evaporation residue discharge and optionally an auxiliary heater; (2) for compressing the mixed vapor generated from the evaporator; and (3) a membrane separator having a membrane selectively permeable to constituents of the mixed vapor, to which the mixed vapor compressed by the compressor is applied. 4. The device according to claim 3, wherein the membrane is a polyimide membrane.